1. Field of the Invention
This invention relates to a binding agent for a pigmentous or resinous composition. More especially this invention relates to a binder composition containing a silicic acid ester, solvent and hardener. This invention is particularly directed to a binder for a pigmentous composition especially a zinc dust paint which does not harden prematurely in a storage vessel and yet dries upon application to a surface within a short period thereafter to provide an anticorrosive coating on a metal such as iron and steel having good hardness qualities. This invention is particularly directed to such a paint composition which fully hardens within about 24 hours. The paints of the present invention are compatible with organic resins.
2. Discussion of The Prior Art
Coating compositions have been described which are based upon organic silicates and zinc dust. Ethyl silicate is named in British Pat. No. 652,136 as organic silicate. It is in the unhydrolyzed state. The coating compositions prepared therefrom by mixing it with solvents, zinc dust and amines as hardeners have a good shelf life, but they take too long to set. The setting time is 4 to 5 hours and is unacceptable in practice. Furthermore, these coating compositions have the disadvantage that they tend to check in coatings more than 50 microns thick.
For the partial removal of these disadvantages, it is proposed in German Pat. No. 12 98 221 to use the ethyl silicate in the hydrolyzed state and use the hydrolyzed solutions together with solutions of polyvinyl butyral resins as binding agents. In this procedure, however, after zinc dust has been incorporated as pigment, the coating composition solidifies within 24 hours. If this system is used, therefore, the zinc dust and the binding agent must be stored separately. This separate storage is a disadvantage for practical application with regard to stocking and with regard to the need to use a mixture immediately after preparation.
The problem has therefore existed of finding a binding agent which, when mixed with zinc dust, will have a very long shelf life in the closed container, but when applied to the substrate will have a very short drying time. Furthermore, the paint prepared therewith must assure ease of use and good adhesion to the substrate, i.e., the pigment must not settle hard in the bottom of the container, and it must be easy to stir up. The paint must be easy to apply by spraying or brushing in a known manner.